Computer Science Unplugged

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Computer Science Unplugged

• Dr. Tom CortinaCarnegie Mellon University

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Computer Science Unplugged

• CS Unplugged is a book of activities that
  illustrate computer science principles without
  using a computer.
• Activities are short and are designed to be
  easily integrated into classes and include
  exercises and lesson plans for teachers.

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CS UNPLUGGED

• The basic edition of Computer Science Unplugged
  has 20 classroom exercises for you to use with
  your students.
• Each exercise has a number of extensions,
  activities and background information.
• All activities can be done without the use of
  computers, but they all demonstrate fundamental
  principles used in computers today.

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FORMATS

• Activities
• Books
• Show
• Web site
• Videos
• Garden

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COUNT THE DOTS

• Data in computers is stored and transmitted as a
  series of zeros and ones.
• How can we represent words and numbers using just
  these two symbols?

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COUNT THE DOTS

• Letters are represented in computers in binary
  also
• A 1 000012
• B 2 000102
• C 3 000112
• D 4 001002
• ...
• Z 26 110102

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COUNT THE DOTS

• 01010
• 10101
• 10011
• 10100
• 01001
• 01110
• 00010
• 01001
• 00101
• 00010
• 00101
• 10010

J U S T I N B I E B E R
A 1 B 2 C 3 D 4 E 5 F 6 G 7 H 8 I 9 J 1
0 K 11 L 12 M 13
N 14 O 15 P 16 Q 17 R 18 S 19 T 20 U 21 V
22 W 23 X 24 Y 25 Z 26
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COUNT THE DOTS

• HAPPY BIRTHDAY, ANTONIO BANDERAS!

Born August 10, 1960
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HAPPY BIRTHDAY?

• HAPPY BIRTHDAY, GEORGE W. BUSH!

Born July 6, 1946
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COLOR BY NUMBERS

• Computer screens are divided up into a grid of
  small dots called pixels (picture elements). In a
  black and white picture, each pixel is either
  black or white.
• Computers store drawings, photographs and other
  pictures using only numbers.
• The following activity demonstrates how a
  computer image can be stored efficiently.

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COLOR BY NUMBERS

• The letter a has been magnified to show the
  pixels. When a computer stores a picture, all
  that it needs to store is which dots are black
  and which are white.

1,3 4,1 1,4 0,1,3,1 0,1,3,1 1,4






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COLOR BY NUMBERS
6,5,2,3 4,2,5,2,3,1 3,1,9,1,2,1 3,1,9,1,1,1 2,1,11
,1 2,1,10,2 2,1,9,1,1,1 2,1,8,1,2,1 2,1,7,1,3,1 1,
1,1,1,4,2,3,1 0,1,2,1,2,2,5,1 0,1,3,2,5,2 1,3,2,5






















































































































































































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COLOR BY NUMBERS

• This technique is called run-length encoding.
• Fax transmission
• Compression of images
• Color encoding
• Use two numbers per run
• First number is how many pixels as before
• Second number is what color (1red, 2green, ...)

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YOU CAN SAY THAT AGAIN!

• Since computers only have a limited amount of
  space to hold information, they need to represent
  information as efficiently as possible. This is
  called compression.
• By coding data before it is stored, and decoding
  it when it is retrieved, the computer can store
  more data, or send it faster through the
  Internet.
• This exercise illustrates how a children's rhyme
  can be compressed.

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YOU CAN SAY THAT AGAIN!

• PITTER PATTER
• PITTER PATTER
• LISTEN TO THE RAIN
• PITTER PATTER
• PITTER PATTER
• ON THE WINDOW PANE

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YOU CAN SAY THAT AGAIN!

• PITTER PATTER
• PITTER PATTER
• LISTEN TO THE RAIN
• PITTER PATTER
• PITTER PATTER
• ON THE WINDOW PANE

BEFORE 78 letters
AFTER29 letters
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YOU CAN SAY THAT AGAIN!

• The arrows and boxes are presented with 2
  numbers.
• PITTER PA(7,4)
• 7 count back 7 positions
• 4 copy 4 letters/spaces
• Sometimes boxes point back to a box with a blank
  inside.

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YOU CAN SAY THAT AGAIN!

• The storage capacity of computers is growing at
  an unbelievable rate.
• In the last 25 years, the amount of storage
  provided on a typical computer has grown about a
  million fold.
• We can compress the data so that it takes up less
  space.
• This exercise uses Ziv-Lempel coding, or LZ
  coding, invented by two Israeli professors in the
  1970s.
• ZIP files, GIF images

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CARD FLIP MAGIC

• When data is stored on a disk or transmitted from
  one computer to another, we usually assume that
  it doesn't get changed in the process. But
  sometimes things go wrong and the data is changed
  accidentally.
• This activity uses a magic trick to show how to
  detect when data has been corrupted, and to
  correct it.

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CARD FLIP MAGIC
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CARD FLIP MAGIC

• This exercise illustrates even parity.
• When computer data is transmitted to another
  computer, extra bits are added so that the number
  of 1s is even.
• The receiving computer can detect if something
  gets messed up during the transmission and can
  correct it if there is one error.
• What happens if there are two errors?

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CARD FLIP MAGIC

• Another example of parity (checksum digits)
• Algorithm
• Add the digits (up to but not including the
  check digit) in the odd-numbered positions
  (first, third, fifth, etc.) together and
  multiply by three.
• Add the digits (up to but not including
  the check digit) in the
  even-numbered positions (second, fourth, sixth,
  etc.) to the result.
• Take the remainder of the result divided by 10
  (modulo operation) and subtract this from 10 to
  derive the check digit.

checksum digit
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LIGHTEST HEAVIEST

• Computers are often used to put lists into some
  sort of order (e.g. names into alphabetical
  order, appointments or e-mail by date, etc.)
• If you use the wrong method, it can take a long
  time to sort a large list into order, even on a
  fast computer.
• In this activity children will discover different
  methods for sorting, and see how a clever method
  can perform the task much more quickly than a
  simple one.

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LIGHTEST HEAVIEST

• Start with 8 containers with different amounts of
  sand or water inside. Seal tightly.
• Children are only allowed to use the scales to
  compare the relative weights of two containers.
• Only two containers can be compared at a time.

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LIGHTEST HEAVIEST

• METHOD 1 is called Selection Sort.
• METHOD 2 is called Quick Sort.
• Generally, quick sort is a lot faster than
  selection sort is.

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TWENTY GUESSES

• Can you read the following sentence?
• Ths sntnc hs th vwls mssng.
• You probably can, because there is not much
  "information" in the vowels.
• This activity introduces a way of measuring
  information content.

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TWENTY GUESSES

• I am thinking of a number between0 and 127.
• Start off with 20 pieces of candy.
• You may only ask questions that have a "yes" or
  "no" answer.
• For each question, you will lose one piece of
  candy.
• Once you guess correctly, you can keep whatever
  candy remains.

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TWENTY GUESSES

• To pick a number between 0 and 127, you only need
  7 guesses.
• Always shoot for the middle number of the range
  and eliminate half the possibilities!
• This concept is called binary search.
• If the number was between 0 and 1,023, you would
  only need 3 additional guesses.
• You can guess a number between 0 and 1,048,575
  in only 20 guesses!

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BEAT THE CLOCK

• This activity illustrates structures used in
  parallel sorting networks.
• Kids sort data by walking through a sorting
  network laid out on the floor.
• The network simulates how a parallel network
  would sort data.
• Kids find out that data can be sorted a lot
  faster in parallel!

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BEAT THE CLOCK
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BEAT THE CLOCKVIDEO ONLINE MATERIAL

• csunplugged.org
• video.google.com
• Search for computer science unplugged
• National Center for Women in Information
  Technology
• Promising Practices flyers

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BATTLESHIPS

• Computers are often required to find information
  in large collections of data.
• Computer scientists study quick and efficient
  ways of doing this.
• This activity demonstrates three different search
  methods so children can compare them.

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BATTLESHIPS

• Battleships are lined up at sea.
• Each battleship has a number that is hidden.
• How many guesses does it take for you to find a
  specific battleship?
• The number of guesses is the child's score.
• The lowest score wins.

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BATTLESHIPS
GAME 1 Ships are randomly ordered.
1630 9263 4127 405 4429
7113 3176 4015 7976
88 3465 1571 8625
2587 7187 5258 8020 1919
141 4414 3056 9118
717 7021 3076 3336
FIND SHIP 717
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BATTLESHIPS
GAME 2 Ships are in increasing order.
33 183 730 911
1927 1943 2200 2215 3451
3519 4055 5548 5655
5785 5897 5905 6118 6296
6625 6771 6831 7151 7806
8077 9024 9328
FIND SHIP 5905
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BATTLESHIPS
GAME 3 Ships are ordered into 10 groups based
onthe sum of the digits of the ship modulo 10.
9308 1478 8417 9434
3121 9503 1114 7019
6519 2469 5105
1524 8112 2000
9050 1265 5711
4200 7153 6028
2385 5832 1917
1990 2502
4135
FIND SHIP 9503
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BATTLESHIPS

• These three games illustrate
• linear search
• binary search
• hashing
• What is the maximum number of guesses required
  for each of these search techniques
• for 26 battleships?
• for n battleships?

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THE MUDDY CITY

• Our society is linked by many networks
  telephone, utilities, roads
• For a particular network, there is usually some
  choice about where the links can be placed.
• This exercise examines a complete network to
  determine the links necessary to connect all the
  components of the network at minimal cost.

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THE MUDDY CITY
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THE MUDDY CITY
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THE MUDDY CITY
a graph
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THE MUDDY CITY
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THE MUDDY CITY
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THE MUDDY CITY

• This exercise illustrates how to build what we
  call the minimal spanning tree.
• A tree does not have any cycles where you can get
  back to where you were before.
• This exercise does not give us the shortest path
  from one location to another.
• But there is another algorithm for that!

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TREASURE HUNT

• Computer programs often need to process a
  sequence of symbols such as words in a document
  or even the text of another program.
• Computer scientists use a Finite State Machine
  (FSM), a set of instructions to see if the
  sequence is acceptable or not.
• This exercise uses the FSM idea using treasure
  maps!

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TREASURE HUNT

• Goal Find Treasure Island, starting from
  Pirates' Island.
• Friendly pirate ships sail along fixed routes
  between islands offering rides to travelers.
• Each island has two departing ships, A and B.
• Determine all possible sequences of ships that a
  traveler can take to arrive at Treasure Island.
• Use your map to record all the ship routes.

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TREASURE HUNT
What is the quickest route?
"directed graph"
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Traffic Light State Machine
Sensor S
?(TM ? S)
START
GR
TM ? S (RESET TY)
TY (RESET TM)
Main St
RY
YR
Side St
? TY
? TY
CMCS
TY (RESET TS)
CM Light Color for Main Street CS Light Color
for Side Street
TS ? S (RESET TY)
RG
TM Boolean Timer for Min. Green Light on Main
St. TS Boolean Timer for Max. Green Light on
Side St. TY Boolean Timer for Yellow Light
? TS ? S
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Cell Phone State Machinein Unified Modeling
Language (UML)
from Object-Oriented Software Development Using
Java by Xiaoping Jia
On
Standby
incoming call
keypad-unlock
power-on
keypad-lock
end
Active
Dialing
Ringing
Off
connection-fail
0-9
talk
Connecting
talk
power-off
Talking
Entry LCDOn() Exit LCDOff()
connection-succeed
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THE ORANGE GAME

• When you have a lot of people using one resource
  (such as cars using roads, or messages getting
  through the Internet), there is the possibility
  of "deadlock".
• A way of working cooperatively is needed to avoid
  this happening.
• This exercise illustrates cooperative problem
  solving and (potentially) deadlock.

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THE ORANGE GAME

• A shared resourcein Pittsburgh

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THE ORANGE GAME

• A shared resourcein New York

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THE ORANGE GAME

• Set up
• Each child is assigned a label or color.
• Give two labeled oranges (or colored balls) to
  each child except one child, who gets only one.
• Each child should not hold his or her own label
  or color initially.
• The children form a circle.
• Goal
• Each child must end up with the orange(s)/ball(s)
  of his or her own label/color.

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THE ORANGE GAME

• Passing Rules
• Only one orange/ball may be held in each hand.
• An orange/ball can only be passed to an empty
  hand of an immediate neighbor in the circle. (A
  child can pass either of their two oranges/balls
  to their neighbor.)
• (optional) No talking.

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THE ORANGE GAME

• Alternate Configurations

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THE ORANGE GAME

• Routing and deadlock are problems in many
  networks, such as road systems, telephone and
  computer systems.
• Engineers spend a lot of time figuring out how to
  solve these problems - and how to design networks
  that make the problems easier to solve.

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MARCHING ORDERS

• Computers are usually programmed using a
  "language", which is a limited vocabulary of
  instructions that can be obeyed.
• One of the most frustrating things about
  programming is that computers always obey the
  instructions to the letter, even if they produce
  a crazy result.
• This activity gives kids some experience with
  this aspect of programming.

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MARCHING ORDERS
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MARCHING ORDERS
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PBJ TIME!

• Is this a good algorithm for making a PBJ
  sandwich?
• 1. Pick up some bread and put it on the table.
• 2. Put peanut butter on the bread.
• 3. Pick up some more bread and put it on the
  table.
• 4. Get jelly out of the jar.
• 5. Spread the jelly on second piece of bread.
• 6. Put the pieces of bread together to make your
  sandwich.

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CS UNPLUGGED

• The teacher's version of Computer Science
  Unplugged is available online at
• http//www.csunplugged.org
• The book is FREE to download and use!
• Additional material will be published soon to add
  even more activities, including video to
  demonstrate how to use these activities
  effectively in your classroom.

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Computer Science Unplugged

• 10100 01000 00001 01110 01011
• 11001 01111 10101
• (THANK YOU)